It has long been known that a fluid curable resin may be in contact with a fluid curing agent, and both components will remain in their fluid condition until the resin and curing agent are mixed together. This phenomenon is caused by the formation of a very thin barrier film between the resin and the curing agent, resulting from reaction between the resin and curing agent at their contiguous surfaces.
This has been used in the production of self-locking threaded fasteners, where contiguous deposits of a fluid curable resin and of a curing agent have been made in thread grooves, and the contiguous deposits mixed by engagement with the threads of a mating threaded member. This is disclosed in Anthony U.S. Pat. No. 3,061,455, and more particularly in my prior U.S. Pat. Nos. 4,059,136 and 4,081,012, where adjacent thread groove convolutions or portions thereof receive the fluid curable resin and the curing agent therefor. In Johnson U.S. Pat. No. 2,939,805, superimposed layers of curable resin and curing agent were deposited in a thread groove, where a "polymeric membrane was substantially immediately formed between the two coatings."
In addition, pressure activated adhesives were formed by micro-encapsulated fluid curable resin in a fluid curing agent as disclosed in Deckert et al. U.S. Pat. No. 3,746,068.
My U.S. Pat. Nos. 4,686,272 and 4,764,579 described a further advance in this art. These patents disclosed a packaged adhesive and a method for producing it. The packaged adhesive provided a user with a single product containing a mixture of epoxy resin and hardener, thus rendering it unnecessary for a user to separately apply the resin and hardener to a surface.
The packaged adhesive disclosed in U.S. Pat. Nos. 4,686,272 and 4,764,579 comprised a mixture of a multiplicity of small, discrete, contiguous deposits of a fluid, uncured but curable resin, and a fluid curing agent for the particular resin. The contiguous deposits were separated by a thin, flexible, rupturable protective barrier film formed in situ by the reaction by the fluid resin and the fluid curing agent initially in contact therewith.
Variations in temperature or in time and temperature were able to cause the thickness and strength of the film to vary. The thickness and uniformity of the film could, however, be controlled by chilling the deposition, and holding it at reduced temperature, for example, -10.degree. F., overnight.
It was later found that it was desirable to control the size of the deposits in order to optimize the effectiveness of the adhesive package for commercial usage. If the deposits were too large, storage or handling of the package might cause the deposits to rupture and cure. Moreover, storage of the package at moderately high temperatures (110.degree. F.) led, in certain situations, to the formation of a reactive crust which detracted from the aesthetic characteristics of the packaged adhesive.
A packaged adhesive, capable of (1) providing both a curable resin and a curing agent for the resin in a single application, and (2) enhanced resistance to curing upon storage or handling would thus be highly desired. The present invention provides such an advance.